Environmental and regulatory initiatives are requiring ever lower levels of both sulfur and aromatics in distillate fuels. For example, proposed sulfur limits for distillate fuels to be marketed in the European Union for the year 2005 is 50 wppm or less. There are also proposed limits that would require lower levels of total aromatics as well as lower levels of multi-ring aromatics found in distillate fuels and heavier hydrocarbon products. Further, the maximum allowable total aromatics level for CARB reference diesel and Swedish Class I diesel are 10 and 5 vol. %, respectively. Further, the CARB reference fuels allows no more than 1.4 vol. % polyaromatics (PNAs). Consequently, much work is presently being done in the hydrotreating art because of these proposed regulations.
However, as the supply of low sulfur, low nitrogen crudes decreases, refineries are processing crudes with greater sulfur and nitrogen contents at the same time that environmental regulations are mandating lower levels of these heteroatoms in products. Consequently, there is a continuous need for hydrotreating catalysts with improved activity and increasingly efficient diesel desulfurization and denitrogenation processes. For example, at a given final sulfur content, a more active catalyst will make it possible to operate under milder process conditions (energy saving) or to increase the life-span of a catalyst between regenerations (cycle length).
In one approach, a family of compounds, related to hydrotalcites, e.g., ammonium nickel molybdates, has been prepared as catalysts to be used in such processes. Whereas X-ray diffraction analysis has shown that hydrotalcites are composed of layered phases with positively charged sheets and exchangeable anions located in the galleries between the sheets, the related ammonium nickel molybdate phase has molybdate anions in interlayer galleries bonded to nickel oxyhydroxide sheets. See, for example, Levin, D., Soled, S. L., and Ying, J. Y., Crystal Structure of an Ammonium Nickel Molybdate prepared by Chemical Precipitation, Inorganic Chemistry, Vol. 35, No. 14, p. 4191-4197 (1996). The preparation of such materials also has been reported by Teichner and Astier, Appl. Catal. 72, 321-29 (1991); Ann. Chim. Fr. 12, 337-43 (1987), and C. R. Acad. Sci. 304 (II), #11, 563-6 (1987) and Mazzocchia, Solid State Ionics, 63-65 (1993) 731-35.
In another approach, U.S. Pat. No. 6,071,402 describes a catalyst for the hydrotreating of hydrocarbon feeds which contains mixed sulfides of a Group VIB metal component, a Group V metal component, and optionally a Group VIII metal component. This publication describes massive catalysts comprising 0.01-100%, preferably 0.05% to 100%, more preferably 0.1% to 100%, of at least one mixed sulfide, the catalyst possibly further containing 0 to 99.99%, preferably 0 to 99.95%, more preferably 0 to 99.9%, of at least one group VIII metal. The preferred supported catalyst of this reference generally comprises, in % by weight with respect to the total catalyst mass, 1% to 99.9%, preferably 5% to 99.5%, more preferably 10% to 99%, of at least one matrix material, 0.1% to 99%, preferably 0.5% to 95%, more preferably 1% to 90%, of at least one mixed sulfide of at least one group VB metal and at least one group VIB metal, the catalyst possibly further containing 0 to 30%, preferably 0 to 25%, more preferably 0 to 20%, of at least one group VIII metal. If a Group VIII metal component is present at all in the catalysts of this reference, it is present in limited amounts. More in particular, in Example 7 a catalyst is prepared which contains 0.070 mole of molybdenum, 0.029 mole of niobium, and 0.029 mole of nickel per 100 grams of catalyst. This catalyst has a Mo:Nb:Ni ratio of 2.4:1:1. In the other examples, the amount of Group VIII metal component in relation to the amount of Group VIB and Group V metal components is even lower.
Also, processes to produce fuels to meet the ever more restrictive Environmental regulations, such as hydrotreating, are well known in the art and typically requires treating the petroleum streams with hydrogen in the presence of a supported catalyst at hydrotreating conditions. The catalyst is usually comprised of a Group VI metal with one or more Group VIII metals as promoters on a refractory support. Hydrotreating catalysts that are particularly suitable for hydrodesulfurization, as well as hydrodenitrogenation, generally contain molybdenum or tungsten on alumina promoted with a metal such as cobalt, nickel, iron, or a combination thereof. Cobalt promoted molybdenum on alumina catalysts are most widely used when the limiting specifications are hydrodesulfurization, while nickel promoted molybdenum on alumina catalysts are the most widely used for hydrodenitrogenation, partial aromatic saturation, as well as hydrodesulfurization.
However, there still exists a need in the art for a process to reduce the sulfur and nitrogen content in distillate boiling range hydrocarbon streams.